Here Comes the Dry Season

A mid-December arctic freeze over the U.S. and Canada pushes a high pressure system south and sets up conditions to accentuate the seasonal shift in the inter-tropical convergence zone amplifying the trade winds across the 10th parallel…

Cactus and yuccas on a Guanacaste hillside. The northwest of Costa Rica looks more like desert than jungle in the dry season

The Pacific side dry season in Costa Rica starts sometime between mid November and early January. On average the middle of December.

This year the rains couldn’t end soon enough.

2017 was already shaping up to be one of the wettest years when in October Tropical Storm Nate destroyed roads and homes and killed and injured people across the Pacific half of the country with record rainfalls. It hasn’t dried out since.

Typical rainfall pattern when warm moist air from the Pacific is pulled across Costa Rica from west to east by a rotating low pressure system in the Caribbean (a tropical storm or hurricane).

The Caribbean is normally much drier during the Pacific and Mountain zones rainiest months (September into December) and was mostly spared. However, now that the winds have shifted the Caribbean has been getting heavy rains and some flooding in mid to late December 2017.

The 2016 rainy season was equally devastating. It started out with heavy rains and severe flooding in the central and southern Pacific and ended with historic hurricane Otto making landfall on the Costa Rica Nicaragua border and crossing from the Caribbean to the Pacific wrecking havoc in the lowlands.

Otto was one of the latest forming hurricanes ever, the first ever hurricane to hit Costa Rica directly, and the first to ever to retain its Atlantic name as a Pacific storm after crossing the continent as a coherent system.

By mid December all that had passed and the Papagayo winds picked up. The arrival of dry season is not like flipping a switch and the rains will taper off not suddenly disappear. As always Guanacaste and the northwest will be drier sooner than the central Pacific and mountains. The Osa and far south Pacific never gets as dry as the north and the Caribbean side doesn’t really have a dry season.

Papagayo Winds Bring Dry Weather to Guanacaste

According to the Costa Rican Meteorological Institute the strong winds out of the northeast that began Dec 18 will continue across Guanacaste, the volcanic range, San José and the Central Valley blowing in the dry season weather patterns by Christmas. When the moist air from the Caribbean moves over land it is driven up cooling as it rises and expands. The moisture is squeezed out as rain on the eastern side of the continental divide leaving hot dry conditions to the west.

Clouds stacked up on the eastern side of the continental divide by the prevailing Papagayo winds (trade winds) in Costa Rica. (from National Meteorological Institute)

The winds typically pick up through January and continue into February frequently reaching 100 kph (60 mph). Even stronger gusts can uproot trees, damage buildings and are responsible for fatalities every year.